Re: [PATCH v3 5/6] powerpc64le: blacklist broken GCC compilers (e.g GCC 7.5.0)

[Florian Weimer <fw@deneb.enyo.de>]

* Paul E. Murphy via Libc-alpha:

> GCC 7.5.0 (BZ# 94200) will refuse to compile if both -mabi=% and
> -mlong-double-128 are passed on the command line.  Surprisingly,
> it will work happily if the latter is not.  For the sake of
> maintianing status quo, test for and blacklist such compilers.

GCC PR reference syntax (as mentioned before), and typo: maintianing

> diff --git a/sysdeps/powerpc/powerpc64/le/configure.ac b/sysdeps/powerpc/powerpc64/le/configure.ac
> index 630086bd88..dde956505c 100644
> --- a/sysdeps/powerpc/powerpc64/le/configure.ac
> +++ b/sysdeps/powerpc/powerpc64/le/configure.ac
> @@ -51,6 +51,21 @@ CFLAGS="$save_CFLAGS"])
>  AS_IF([test "$libc_cv_compiler_powerpc64le_ice" != "yes"],
>        [critic_missing="$critic_missing __builtin_signbit is broken. GCC 7.4 or newer is required to resolve (BZ 83862)."])
>  
> +dnl Some old compiler versions give out error messages when combining
> +dnl -mabi=% and -mlong-double-128.  i.e GCC 7.5.0 (BZ# 94200)

PR reference.

> +AC_CACHE_CHECK([if $CC compiles with -mabi=ieeelongdouble and -mlong-double-128],
> +	       libc_cv_compiler_powerpc64le_ldbl128_mabi, [dnl
> +save_CFLAGS="$CFLAGS"
> +CFLAGS="$CFLAGS -mabi=ieeelongdouble -mlong-double-128"
> +AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
> +long double x;
> +]])],
> +		  [libc_cv_compiler_powerpc64le_ldbl128_mabi=yes],
> +		  [libc_cv_compiler_powerpc64le_ldbl128_mabi=no])
> +CFLAGS="$save_CFLAGS"])
> +AS_IF([test "$libc_cv_compiler_powerpc64le_ldbl128_mabi" == "no"],
> +      [critic_missing="$critic_missing The compiler must support -mabi=ieeelongdouble and -mlongdouble simultaneously."])
> +
>  # Binutils (objcopy) 2.26 or newer required to support the --update-section
>  # feature for fixing up .gnu.attribute section with IEEE ldbl.
>  AC_CHECK_PROG_VER(OBJCOPY, $OBJCOPY, --version,

This change looks reasonable to me.

Maybe add the @c comment to the install.texi file with this patch?
Something like this:

@c See this autoconf check:
@c if $CC compiles with -mabi=ieeelongdouble and -mlong-double-128